Golf balls, whether of solid or wound construction, generally include a core and a cover. It is known in the art to modify the properties of a conventional solid ball by altering the typical single layer core and single cover layer construction to provide a ball having at least one mantle layer disposed between the cover and the core. The core may be solid or liquid-filled, and may be formed of a single layer or one or more layers. Covers, in addition to cores, may also be formed of one or more layers. These multi-layer cores and covers are sometimes known as “dual core” and “dual cover” golf balls, respectively. Additionally, many golf balls contain one or more intermediate layers that can be of solid construction or, in many cases, be formed of a tensioned elastomeric winding, which are referred to as wound balls. The difference in play characteristics resulting from these different types of constructions can be quite significant. The playing characteristics of multi-layer balls, such as spin and compression, can be tailored by varying the properties of one or more of these intermediate and/or cover layers.
Manufacturers generally provide the golf ball with a durable cover material, such as an ionomer resin, or a softer cover material, such as polyurethane. Chemically, ionomer resins are a copolymer of an olefin and an α,β-ethylenically-unsaturated carboxylic acid having 10-90% of the carboxylic acid groups neutralized by a metal ion and are distinguished by the type of metal ion, the amount of acid, and the degree of neutralization. Commercially available ionomer resins include copolymers of ethylene and methacrylic or acrylic acid neutralized with metal salts. Examples include SURLYN® from E.I. DuPont de Nemours and Co. of Wilmington, Del. and IOTEK® from Exxon Corporation of Houston, Tex.
Surrounding the core with an ionomeric cover material provides a ball that is virtually indestructible by golfers. The core/cover combination permits golfers to impart a high initial velocity to the ball that results in improved distance.
Polyurethanes are used in a wide variety of applications including adhesives, sealants, coatings, fibers, injection molding components, thermoplastic parts, elastomers, and both rigid and flexible foams. Polyurethane can be produced by the product of a reaction between a polyurethane prepolymer and a curing agent. The polyurethane prepolymer is generally a product formed by a reaction between a polyol and a diisocyanate. The curing agents used previously are typically diamines or glycols. A catalyst is often employed to promote the reaction between the curing agent and the polyurethane prepolymer.
Since about 1960, various companies have investigated the usefulness of polyurethane as a golf ball cover material. U.S. Pat. No. 4,123,061 teaches a golf ball made from a polyurethane prepolymer of polyether and a curing agent, such as a trifunctional polyol, a tetrafunctional polyol, or a fast-reacting diamine. U.S. Pat. No. 5,334,673 discloses the use of two categories of polyurethane available on the market, i.e., thermoset and thermoplastic polyurethanes, for forming golf ball covers and, in particular, thermoset polyurethane covered golf balls made from a composition of polyurethane prepolymer and a slow-reacting amine curing agent, and/or a difunctional glycol.
Additionally, U.S. Pat. No. 3,989,568 discloses a three-component system employing either one or two polyurethane prepolymers and one or two polyol or fast-reacting diamine curing agents. The reactants chosen for the system must have different rates of reactions within two or more competing reactions.
The color instability caused by both thermo-oxidative degradation and photodegradation typically results in a “yellowing” or “browning” of the polyurethane layer, an undesirable characteristic for urethane compositions are to be used in the covers of golf balls, which are generally white.
U.S. Pat. No. 5,692,974 to Wu et al. discloses golf balls which have covers and cores and which incorporate urethane ionomers. The polyurethane golf ball cover has improved resiliency and initial velocity through the addition of an alkylating agent such as t-butyl chloride to induce ionic interactions in the polyurethane and thereby produce cationic type ionomers. UV stabilizers, antioxidants, and light stabilizers may be added to the cover composition.
U.S. Pat. No. 5,484,870 to Wu discloses a golf ball cover comprised of a polyurea. Polyureas are formed from reacting a diisocyanate with an amine.
U.S. Pat. No. 5,823,890 to Maruko et al., discloses a golf ball formed of a cover of an inner and outer cover layer compression molded over a core. The inner and outer cover layers should have a color difference ΔE in Lab color space of up to 3.
U.S. Pat. No. 5,840,788 to Lutz et al. discloses a UV light resistant, visibly transparent, urethane golf ball topcoat composition for use with UV curable inks. The topcoat includes an optical brightener that absorbs at least some UV light at wavelengths greater than about 350 nm, and emits visible light, and a stabilizer package. The light stabilizer package includes at least one UV light absorber and, optionally, at least one light stabilizer, such as a HALS.
U.S. Pat. No. 5,494,291 to Kennedy discloses a golf ball having a fluorescent cover and a UV light blocking, visibly transparent topcoat. The cover contains a fluorescent material that absorbs at least some UV light at wavelengths greater than 320 nm and emits visible light.
Colored golf balls have been produced for many years. In the 1960s Spalding produced a yellow range ball with a blended cover that included polyurethane.
U.S. Pat. No. 4,798,386, to Berard, makes reference to white cores and clear covers and even locating decoration on the core to be visible through the clear cover. The Berard concept requires a core which has a satisfactory hue to achieve the desired finished ball coloration. A polybutadiene rubber core of such a color has never been produced and as such, clear cover 2-pc ball have had limited market success.
U.S. Pat. No. 4,998,734 to Meyer, describes a golf ball with a core, a clear cover and “layer interdisposed therebetween.” However, the intermediate layer described is a thin layer of paper or plastic material whose purpose is only to bear textural, alphanumeric or graphical indicia. Meyer teaches that the layer should be sufficiently thin to permit substantial transference of impact forces from the cover to the core without substantially reducing the force.
The Pro Keds “Crystal π” golf ball appeared in the Japanese market. It had a white core bearing the ball markings and a clear Surlyn cover. This ball had a very thick clear cover (>0.065″) and the surface dimple coverage was very low.
In the early 1990s, Acushnet made clear Surlyn cover, two-piece Pinnacle Practice balls. The covers were 0.050″ thick.
A prototype Wilson Surlyn covered two-piece ball, “Quantum”, of a design similar to the Pro Keds ball was found in the US in the late 1990s. The cover was greater than 0.065 inches thick.
U.S. Pat. No. 5,442,680, Proudfit is directed to a golf ball with a clear ionomer cover. The patent requires a blend of ionomers with different cations.
In the early 1990s a solid one-piece urethane golf ball having a hole for the insertion of a chemi-luminescent tube was sold as a “Night Golf” ball. It was relatively translucent to create the glow, but it was far from having the performance characteristics of standard golf balls.
Two-piece balls have been sold under the tradename “Glow Owl” which utilize a white core and a cover with glow in the dark materials. This ball is believed to embody the technology described in U.S. Pat. No. 5,989,135 to Welch, which describes a “partially translucent” cover.
At the January 2001 PGA Show, Wilson displayed samples of “iWound” golf balls with clear covers. They were not balls for actual play but mock-ups used to display their new “lattice wound” technology. The lattice (discontinuous inner cover layer) was Hytrel and the Surlyn outer cover layer was clear. Both the Hytrel lattice and red core were visible through the clear cover. No markings were on the core or lattice.
To date, it has been difficult for manufacturers to properly attain the desired long-term appearance of polyurethane compositions used in golf ball covers without adversely affecting golf ball performance. Many golf balls have at least one layer of “paint” covering the cover material. This long-felt problem in the golf ball art has now led the Applicants to seek a desirable formulation of a polyurethane composition suitable for use in golf ball covers that exhibits improved properties and allows for substantially different looking golf balls